A major challenge of detergent development for industry, restaurants, and homes is the successful removal of soils that are resistant to conventional treatment and the elimination of chemicals that are not compatible with the surroundings. One such soil is protein, and one such chemical is chlorine or chlorine yielding compounds, which can be incorporated into detergent compounds or added separately to cleaning programs for protein removal. Protein soil residues, often called protein films, occur in all food processing industries, in restaurants, in laundries, and in home cleaning situations.
In the past, chlorine has been employed to degrade protein by oxidative cleavage and hydrolysis of the peptide bond, which breaks apart large protein molecules into smaller peptide chains. The conformational structure of the protein disintegrates, dramatically lowering the binding energies, and effecting desorption from the surface, followed by solubilization or suspension into the cleaning solution. The use of chlorinated detergent is not without problems, such as harshness and corrosion. In addition, a new issue may force change upon both the industry, consumers, and detergent manufacturers: the growing public concern over the health and environmental impacts of chlorine and organochlorines.
Detersive enzymes represent an alternative to chlorine and organochlorines. Enzymes have been employed in cleaning compositions since early in the 20th century. However, it took years of research, until the mid 1960's, before enzymes like bacterial alkaline proteases were commercially available and which had all of the minimum pH stability and soil reactivity for detergent applications. Patents issued through the 1960s related to use of enzymes for consumer laundry pre-soak or wash cycle detergent compositions and consumer automatic dishwashing detergents. Early enzyme cleaning products evolved from simple powders containing alkaline protease to more complex granular compositions containing multiple enzymes to liquid compositions containing enzymes. See, for example, U.S. Pat. No. 3,451,935 to Roald et al., issued Jun. 24, 1969 and U.S. Pat. No. 3,519,570 to McCarty issued Jul. 7, 1970.
Liquid detergent compositions containing enzymes have advantages compared to dry powder forms. Enzyme powders or granulates tended to segregate in these mechanical mixtures resulting in non-uniform, and hence undependable, product in use. In dry compositions, humidity can cause enzyme degradation. Dry powdered compositions are not as conveniently suited as liquids for rapid solubility or miscibility in cold and tepid waters nor functional as direct application products to soiled surfaces. For these reasons and for expanded applications, it became desirable to have liquid enzyme compositions.
Although water is a desirable solvent for liquid cleaning compositions, there are problems in formulating enzymes into aqueous compositions. Enzymes generally denature or degrade in an aqueous medium resulting in the serious reduction or complete loss of enzyme activity. This instability results from at least two mechanisms. Enzymes have three-dimensional protein structure which can be physically or chemically changed by other solution ingredients, such as surfactants and builders, causing loss of catalytic effect. Alternately when protease is present in the composition, the protease will cause proteolytic digestion of the other enzymes if they are not proteases; or of itself via a process called autolysis. The prior art discloses attempts to deal with these aqueous induced enzyme stability problems by minimizing water content or altogether eliminating water from the liquid enzyme containing composition. See, for example, U.S. Pat. No. 3,697,451 to Mausner et al. issued Oct. 10, 1972 and U.S. Pat. No. 4,753,748 to Lailem et al. issued Jun. 28, 1988.
The prior art also discloses the previous uses of enzymes in a two part system where the first part contained the surfactant and enzyme and the second part contained the builder and alkalinity source. See U.S. Pat. Nos. 6,197,739 and 5,064,561. A two part system was necessary due to the instability of the enzyme. Also important was the fact that the activity of protease enzymes typically peaks between the pH of about 8.6 and about 10.5 and when placed in an alkaline environment, the pH promoted enzyme activity in turn causing the enzyme to hydrolyze and inactivate itself in a concentrate. A need exists for a stabilization system which would allow the alkalinity to be contained in the same product as the enzyme.
In order to market an aqueous enzyme composition, the enzyme must be stabilized so that it will retain its functional activity for prolonged periods of (shelf-life or storage) time. If a stabilized enzyme system is not employed, an excess of enzyme is generally required to compensate for expected loss. However, enzymes are expensive and are in fact the most costly ingredients in a commercial detergent even though they are present in relatively minor amounts. Thus, it is no surprise that various methods of stabilizing enzyme-containing, aqueous, liquid detergent compositions are described in the patent literature. There remains a need, however, for additional methods and compositions for stabilizing enzymes in cleaning compositions, particularly at high concentrations of water and/or alkaline pH.